The present disclosure relates to an electromagnetic interference blocking device and an assembly including same. More particularly, the present disclosure relates to an electromagnetic interference blocking device for blocking electromagnetic interferences among transmission lines formed on a circuit board, and an assembly having the device mounted on a circuit board.
When a current flows through a signal line, an electromagnetic field may be generated. The electromagnetic field, in turn, may generate an induced current/voltage in a neighboring signal line, which degrades performance of the neighboring signal line. Since the strength of the induced current/voltage in the neighboring signal line is proportional to the frequency of current/voltage applied in the signal line, performance degradation due to the induced current/voltage hardly occurs among signal lines in a DC circuit. However, in a circuit using a high frequency signal, such as a radio frequency (RF) signal, the impact of the induced current/voltage on performance of a neighboring signal line may become pronounced.
The above phenomenon, referred to as electromagnetic coupling, includes inductive coupling and capacitive coupling. The induced voltage (Vnoise) and the induced current (Inoise) may be determined from Equations (1) and (2), where Lm and Cm represent mutual inductance and mutual capacitance, respectively:
                              V          noise                =                              L            m                    ⁢                                    ⅆ              I                                      ⅆ              t                                                          (        1        )                                          I          noise                =                              C            m                    ⁢                                    ⅆ              V                                      ⅆ              t                                                          (        2        )            
As can be seen from Equations (1) and (2), the more frequently changes occur in current/voltage (i.e., the higher the frequency of current/voltage), the stronger the induced voltage/current becomes. However, the strength of the induced voltage/current cannot be controlled by simply changing the frequency of the voltage/current. This is particularly true in communication device circuitry, because the frequency range is determined based on bandwidth to be used and/or use of the entire circuitry. For example, most cellular phones operate in ultra high frequency (UHF) band ranging from 300 MHz to 3 GHz, which cannot be changed. Accordingly, the induced voltage/current can be reduced only by reducing the mutual inductance Lm and the mutual capacitance Cm.
For example, the mutual inductance and/or the mutual capacitance may be reduced by increasing the distance between the signal line and the neighboring signal line. However, this results in increasing the size of the circuitry, and therefore is generally not a desirable approach.
In an effort to reduce the electromagnetic coupling without increasing the size of the circuitry, mounting an electromagnetic shield between neighboring signal lines on a printed circuit board (PCB) for isolating the signal lines from each other has been proposed. However, such electromagnetic shield has a drawback with respect to mass-production of circuitry because an additional process, such as soldering or welding, is necessary for mounting the electromagnetic shield on the PCB. Furthermore, it would be difficult to detach the mounted electromagnetic shield from the PCB, for example, in order to rearrange positioning of the electromagnetic shield and/or circuitry.